Cellular Metabolism
glycolysis Krebs Cycle and Electron Transport Chain
http://www.chem.purdue.edu/courses/chm333/web%20Site%202.htm
metabolism
I. Metabolism = The sum total of all chemical reactions that occur in an organism.
A. Anabolism = building large molecules from smaller ones, requiring energy. (EX: Photosynthesis)
B. Catabolism = breaking down large molecules into smaller ones, releasing energy. (EX: Respiration)
II. Control of Metabolic Reactions
A. Enzymes control the rates of all the metabolic reactions of the cell.
B. Enzyme Action
1. Enzymes = complex proteins that lower the energy needed by a reaction so it can proceed more rapidly.
2. Enzymes work in small quantities and are recycled by the cell.
3. Each enzyme is specific, acting on only one kind of substrate.
a. Substrate = molecule that an enzyme will change.
b. Active sites = place on enzyme that combines with the substrate to cause a reaction to occur.
4. Lock-and-Key Model of Enzyme Action:
* The enzyme is like a key that fits into a specific lock(substrate) to either open or close the lock (break or bond the molecule). The enzyme can be used again and again!
C. Factors That Alter Enzyme Action
1. Enzymes can be denatured (altered) by heat, pH extremes, chemicals, electricity, radiation, and by other causes.
2. The speed of enzymatic reactions depends on the number of enzyme and substrate molecules available.
Cellular respiration
Cellular respiration is the enzymatic breakdown of glucose (C6H12O6) in the presence of oxygen (O2) to produce cellular energy - ATP
C6H12O6 + 6O2 -->6 CO2 + 6H2O + 36 ATP
glucose + oxygen --> carbon dioxide + water + ATP
1.Glycolysis:
a) 6 carbon glucose is split into two 3 carbon pyruvates
b) anaerobic - proceeds whether or not O2 is present ; O2 is not required
d) net yield of 2 ATP per glucose molecule
e) net yield of 2 NADH per glucose ---> sent to the ETC in mitochondria
The pyruvic acid diffuses into the inner compartment of the mitochondrion where a transition reaction occurs that serves to prepare pyruvic acid for entry into the next stage of respiration, this converts them an acetyl CoA which enters the Kreb's cycle.
If oxygen is not present, pyruvate is converted to lactic acid in the cytoplasm -- anaerobic respiration
2. Citric Acid or Krebs Cycle
a)occurs in the inner mitochondrial matrix
b) an aerobic process; will proceed only in the presence of O2
c) net yield of 2 ATP per glucose molecule
d) net yield of 6 NADH and 2 FADH2 (NAD+ is reduced to NADH, FAD+ is reduced to FADH)
e) in this stage of cellular respiration, the oxidation of glucose to CO2 is completed.
3. Electron Transport System:
a) consists of a series of enzymes on the inner mitochondrial membrane
b) electrons are released from NADH and from FADH2 and as they are passed along the series of enzymes, they give up energy which is used to fuel a process called chemiosmosis, which drives the process of ATP synthesis using an enzyme called ATPase.
c) net yield of 32 ATP per glucose molecule
d) 6 H2O are formed when the electrons unite with O2* at the end of electron transport chain.
* Note: This is the function of oxygen in living organisms!
Food for Thought
1. What is the purpose of cellular respiration?
2. Where does cellular respiration occur within the cell?
3. What is the waste product of cellular respiration?
4. Comparing photosynthesis to respiration
a) Where does each occur?
b) What are the products of each?
c) What compounds are needed to start the process
d) What is the function of the Electron Transport Chain in each process
e) Describe the role of ATPase in photosynthesis and cellular respiration.
Photosynthetic Organisms
A. Photosynthesis Transforms Solar Energy
B. Organic molecules built by photosynthesis provide both the building blocks and energy for cells.
C. Plants use the raw materials: carbon dioxide and water
D. Chloroplasts carry out photosynthesis
E. Chlorophylls and other pigments involved in absorption of solar energy reside within thylakoid membranes of chloroplasts
Plants as Solar Energy Converters
A. Solar Radiation - Only 42% of solar radiation that hits the earth’s atmosphere reaches surface; most is visible light.
B. Photosynthetic Pigments - Pigments found in chlorophyll absorb various portions of visible light; absorption spectrum.
1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.
2. Both chlorophylls absorb violet, blue, and red wavelengths best.
3. Very little green light is absorbed; most is reflected back; this is why leaves appear green.
4. Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions.
5. When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through.
Additional Resources for Photosynthesis
C. Absorption and action spectrum - A spectrophotometer measures the amount of light that passes through a sample of pigments.
1) As different wavelengths are passed through, some are absorbed.
2) Graph of percent of light absorbed at each wavelength is absorption spectrum.
3) Photosynthesis produces oxygen; production of oxygen is used to measure the rate of photosynthesis.
4) Oxygen production and, therefore, photosynthetic activity is measured for plants under each specific wavelength; plotted on a graph, this produces an action spectrum.
5) Since the action spectrum resembles absorption spectrum, this indicates that chlorophylls contribute to photosynthesis.
D. Photosynthetic Reaction
1. In 1930 C. B. van Niel showed that O2 given off by photosynthesis comes from water and not from CO2.
2. The net equation reads:
E. Two Sets of Reactions in Photosynthesis
Light Dendendent and Light Independent
1. Light reactions cannot take place unless light is present. They are the energy-capturing reactions.
b. Chlorophyl within thylakoid membranes absorbs solar energy and energizes electrons.
c. Energized electrons move down the electron transport system; energy is captures and used for ATP production.
d. Energized electrons are also taken up by NADP+, becoming NADPH.
2. Calvin Cycle Reactions
a. These reactions take place in the stroma; can occur in either the light or the dark.
b. These are synthesis reactions that use NADPH and ATP to reduce CO2.
c. The end product is glucose which can be used by the plant
